Cancer is one of the leading causes of death in humans and while standard chemotherapy, radiotherapy and surgical intervention successfully reduce tumor load in many cases, resistance to chemotherapeutic intervention is not uncommon, especially in solid tumors. Resistance develops following exposure to chemotherapy and further impedes tumor regression and cure. It is this chemotherapy resistance leading to treatment failure that accounts for the high mortality rates in cancer.
The molecular basis of chemotherapy resistance is largely genetic, and can take many forms. Many mutations responsible for the initial development of tumors may also contribute to drug resistance. For example, loss of DNA mismatch repair (MMR) gene function has been associated with a more rapid emergence of clinical drug resistance in some cancers (de las Alas M. M., et al., 1997. J Natl Canc Inst 89:1537-41; Lin X. and Howell, S. B. 1999. Mol Pharmacol 56:390-5), and mutations in the K-ras gene (found in approximately 40% of adenomatous polyps and adenocarcinomas) are associated with an increased relapse rate, mortality and a poor chemotherapeutic response (Arber N. et al. 2000. Gastroenterology 118:1045-1050). Aberrant expression and dysregulation of proteins involved in the normally tightly regulated cell replication cycle may also be protective of tumors—these proteins may be loosely referred to as ‘oncogenes’ in the literature. Gene products p21 and p27, for example, have been shown to protect tumors from undergoing apoptosis elicited by various anticancer agents (Waldman T. et al., 1996. Uncoupling of S phase and mistosis induced by anticancer agents in cells lacking p21. Nature 381:713 716; St. Croix B. et al., 1996. Nature Med 1996, 2:1204-1210). Adhesion molecules, such as E-cadherin, may also confer resistance to cells exposed to chemotherapeutic agents (Skoudy A, et al., 1996. Biochem J 317: 279-84.). The mechanisms involved in therapeutic resistance are varied and may be very complex.
Chemosensitizers may act in concert with the chemotherapeutic agent, or may serve to counteract resistance mechanisms in the cell. Existing chemosensitizers include small molecule drugs such as photosensitizers or drug efflux pump inhibitors, and more recently, antisense oligonucleotides. New compounds with chemosensitizing activity include U.S. Pat. No. 5,776,925 and WO 02/00164, which provide examples of novel chemical compounds that enhance cytotoxicity of therapeutic agents.
U.S. Pat. No. 6,001,563 provides for a method for identifying chemical compounds that may have chemosensitizing activity.
Antisense sequences with chemosensitizing activity—often specifically targeting oncogenes—are varied and may be found for almost any target. For example, survivin is a protein that modulates apoptosis and is frequently overexpressed in cancer cells (Krajewska, M. et al. 2003. Clin Cancer Res 9:4914; Kaur, P. et al. 2004. Arch Pathol Lab Med 128:39; Shariat, S. F. et al., 2004. Urine detection of surviving is a sensitive marker for the noninvasive diagnosis of bladder cancer. J Urol 171: 626). Antisense survivin oligonucleotides have been demonstrated to downregulate expression of Survivin, and sensitize cells to chemotherapeutic agents such as docetaxel and etopotide (Hayashi, N. et al., 2005. Prostate 15:10-19).
Similarly, cancer therapy sensitizers may act in concert with cancer therapeutic agents, e.g., radiotherapy, or may serve to counteract resistance mechanisms in the cell to the cancer therapeutic agent.
Secreted protein acidic and rich in cysteine (SPARC) is one example of a gene with significantly decreased expression in multidrug resistant cell lines in vitro, with a possible tumor suppressor role (Tai, I. T. et al. 2005. J. Clin Invest. 115:1492-1502). SPARC, also known as osteonectin, belongs to a family of matricellular proteins having counter-adhesive properties, disruptive of cell-matrix interactions (Bornstein P. 1995. J. Cell Biol 130:503-6; Sage E. H. and Bornstein P. 1991. J Biol Chem; 266:14831-4).
SPARC has been demonstrated to play a role in bone mineralization, tissue remodeling, endothelial cell migration, morphogenesis and angiogenesis (Latvala T. et al., 1996. Exp Eye Res. 63:579-84; Hasselaar P. and Sage E H. 1992. J Cell Biochem. 49:272-83; Mason I. J. et al. 1986. EMBO J. 5:1831-7; Strandjord T. P. et al. 1995. Am J Respir Cell Mol Biol. 13:279-87; Kupprion C, et al., 1998. J Biol Chem. 273:29635-40; Lane T. F. et al. 1994. J Cell Biol. 125:929-43).
Some N-terminal and C-terminal peptides of murine SPARC that block SPARC-mediated anti-spreading activity in bovine aortic endothelial cells in culture are described (Lane T F and Sage, E H 1990. J. Cell Biol 111:3065-3076).
A peptide corresponding to one segment of the follistatin domain inhibits endothelial cell migration in vitro, and angiogenesis in a rat corneal assay model (Chlenski et al 2004. Cancer Res. 64:7420-7425)
Some peptides corresponding to the cationic region of murine SPARC and act as stimulators of capillary growth in vitro and in vivo. However, Cu2+ binding activity alone does not appear to be sufficient for a peptide to stimulate angiogenesis (Lane et al 1994. J Cell Biol 125:929-943).
Additional studies suggest that cleavage of SPARC by MMP-3 results in peptides that affect angiogenesis (Sage et al. 2003 J. Biol Chem 287: 37849-37857).
SPARC also has a role in malignancy, as variable gene and protein expression of SPARC have been linked to cancer progression in a number of tumors (Yiu, G. K., et al., 2001. Am J. Pathol 159:609-622; Rempel S. A. et al., 2001. J Neurooncol 53:149-60; Schultz C. et al., 2002. Cancer Res 62:6270-7; Porter P. L. et al., 1995. J Histochem Cytochem 43:791-800). Studies in SPARC knockout animals reveal that loss of SPARC enhances growth of tumor xenografts of pancreatic and lung cancers (Puolakkainen P. A. et al. 2004. Mol Cancer Res 2:215-24; Brekken R. A. et al. 2003. J Clin Invest 111:487-95).
The use of the intact, isolated SPARC protein as a chemosensitizer is described by WO 2004/064785.